Receiver, communication system, and channel estimation method

ABSTRACT

A receiver includes a channel estimation unit that calculates channel estimation values of symbols containing pilot signals from signals transmitted by a plurality of antennas to obtain channel estimation values of symbols in the same positions of the antennas, a de-precoding unit that de-precodes the channel estimation values of the antennas calculated by the channel estimation unit to calculate effective channel estimation values, and a time-direction interpolation unit that performs time-direction interpolation using the effective channel estimation values calculated by the de-precoding unit to calculate effective channel estimation values of symbols other than the symbols containing pilot signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2009-228843, filed on Sep. 30,2009, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to a receiver, a communication system, anda channel estimation method.

BACKGROUND

In wireless communications using the Orthogonal Frequency DivisionMultiplexing (OFDM) system, the receiver estimates the channel usingpilot signals. The pilot signals here refer to signals known by both thetransmitter and receiver. For example, in a standard for high-speedmobile communications, the Long Term Evolution (LTE), pilot signals arearranged at given intervals both in the frequency direction and in thetime direction.

In the case of four transmitting antennas, pilot signals are arranged atintervals of certain subcarriers in each sub-frame according to the LTEtransmission format. For example, with regard to the transmittingantennas having the transmitting antenna numbers 0 and 1, pilot signalsare arranged at intervals of six subcarriers in the OFDM symbols havingthe symbol numbers 0, 4, 7, and 11. With regard to the transmittingantennas having the transmitting antenna numbers 2 and 3, pilot signalsare arranged at intervals of six subcarriers in OFDM symbols having thesymbol numbers 1 and 8.

One known example of such a channel estimation method using pilotsignals is a method of obtaining a channel estimation value by bothfrequency-direction interpolation and time-direction interpolation.Specifically, the receiver estimates the channels of resource elements(REs) where pilot signals are arranged. The receiver then performsfrequency-direction interpolation and time-direction interpolation onthe channel estimation values of the REs where pilot signals arearranged so as to obtain the channel estimation values of REs where nopilot signals are arranged.

On the other hand, in wireless communication systems (multiple-inputmultiple-output (MIMO)) using multiple transmitting antennas andreceiving antennas, the transmitter precodes signals transmitted by thetransmitting antennas so that the receiver may readily divide thetransmitted signals.

For example, x′=Px where x represents a yet-to-be-precoded, transmittedsignal, P represents a precoding matrix (or vector), and x′ represents aprecoded, transmitted signal.

In addition, y=Hx′=HPx where H represents a channel matrix and yrepresents a received signal. The receiver estimates the channel toobtain a channel estimation value matrix H′ and then de-precodes thechannel estimation value matrix to calculate H^(˜)=H′P to obtain aneffective channel estimation value matrix H^(˜). The receiver performsdemodulation using the obtained effective channel estimation valuematrix H^(˜).

Hereafter, the channel estimation process and de-precoding process willbe described using an example illustrated in FIG. 10. FIG. 10 is adrawing explaining the related art and illustrates the process flow in acase where channel estimation by frequency-direction interpolation,channel estimation by time-direction interpolation, and de-precoding areperformed in the presented order so as to obtain the effective channelestimation value corresponding to one sub-frame. Here, it is assumedthat four transmitting antennas and one layer are provided according tothe LTE transmission format.

As illustrated in FIG. 10, the receiver estimates the channels of REswhere pilot signals are arranged. The receiver then performsfrequency-direction interpolation using OFDM symbols containing pilotsignals so as to obtain the channel estimation values of all the REs ineach OFDM symbol.

The receiver then obtains the channel estimation values of symbolsbetween each two OFDM symbols containing pilot signals by time-directioninterpolation. Specifically, the receiver obtains the channel estimationvalues of the symbols having the symbol numbers 0, 4, 7, and 11 of thetransmitting antennas having the transmitting antenna numbers 0 and 1and those of the symbols having the symbol numbers 1 and 8 of thetransmitting antennas having the transmitting antenna numbers 2 and 3 byfrequency-direction interpolation, and obtains the channel estimationvalues of the other symbols by linear interpolation.

The channel estimation value after time-direction interpolation isobtained by Formulas (35) and (36) below. In the formulas, a representsa receiving antenna number, b represents a transmitting antenna number,n represents a sub-frame number, t represents a symbol number, and h (a,b, n, t, i) represents the channel estimation value of the subcarriernumber i after frequency-direction interpolation. Note that the channelestimation value after the time-direction interpolation is representedby h (a, b, n, t, i) as with the channel estimation value afterfrequency-direction interpolation. This is because time-directioninterpolation is performed with respect to the symbols whose channelestimation value has not been obtained in frequency-directioninterpolation.

$\begin{matrix}{{h\left( {a,b,n,t,i} \right)} = \left\{ \begin{matrix}{h\left( {a,b,n,0,i} \right)} & \left( {{b = 0},1,{t = 0}} \right) \\{{\frac{4 - t}{4}{h\left( {a,b,n,0,i} \right)}} + {\frac{t}{4}{h\left( {a,b,n,4,i} \right)}}} & \left( {{b = 0},1,{t = 1},2,3} \right) \\{h\left( {a,b,n,4,i} \right)} & \left( {{b = 0},1,{t = 4}} \right) \\{{\frac{7 - t}{3}{h\left( {a,b,n,4,i} \right)}} + {\frac{t - 4}{3}{h\left( {a,b,n,7,i} \right)}}} & \left( {{b = 0},1,{t = 5},6} \right) \\{h\left( {a,b,n,7,i} \right)} & \left( {{b = 0},1,{t = 7}} \right) \\{{\frac{11 - t}{4}{h\left( {a,b,n,7,i} \right)}} + {\frac{t - 7}{4}{h\left( {a,b,n,11,i} \right)}}} & \left( {{b = 0},1,{t = 8},9,10} \right) \\{h\left( {a,b,n,11,i} \right)} & \left( {{b = 0},1,{t = 11}} \right) \\{{\frac{14 - t}{3}{h\left( {a,b,n,11,i} \right)}} + {\frac{t - 11}{4}{h\left( {a,b,{n + 1},0,i} \right)}}} & \left( {{b = 0},1,{t = 12},13} \right)\end{matrix} \right.} & (35) \\{{h\left( {a,b,n,t,i} \right)} = \left\{ \begin{matrix}{{\frac{1}{7}{h\left( {a,b,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,b,n,1,i} \right)}}} & \left( {{b = 2},3,{t = 0}} \right) \\{h\left( {a,b,n,1,i} \right)} & \left( {{b = 2},3,{t = 1}} \right) \\{{\frac{8 - t}{7}{h\left( {a,b,n,1,i} \right)}} + {\frac{t - 1}{7}{h\left( {a,b,n,8,i} \right)}}} & \left( {{b = 2},3,{t = 2},3,\ldots \mspace{11mu},7} \right) \\{h\left( {a,b,n,8,i} \right)} & \left( {{b = 2},3,{t = 8}} \right) \\{{\frac{15 - t}{7}{h\left( {a,b,n,8,i} \right)}} + {\frac{t - 8}{7}{h\left( {a,b,{n + 1},1,i} \right)}}} & \left( {{b = 2},3,{t = 9},\ldots \mspace{11mu},13} \right)\end{matrix} \right.} & (36)\end{matrix}$

Subsequently, as illustrated in FIG. 10, the channel estimation valuesof the four transmitting antennas are de-precoded to obtain theeffective channel estimation value corresponding to one layer. Theeffective channel estimation value h˜(a, l, n, t, i) after de-precodingwhere a represents a receiving antenna number, l represents a layernumber, n represents a sub-frame number, t represents a symbol number,and i represents a subcarrier number is obtained by Formula (37) below.When Formulas (35) and (36) are substituted into Formula (37), theeffective channel estimation values are obtained as indicated byFormulas (38) to (51) below.

$\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,t,i} \right)} = {{V_{0}{h\left( {a,0,n,t,i} \right)}} + {V_{1}{h\left( {a,1,n,t,i} \right)}} + {V_{2}{h\left( {a,2,n,t,i} \right)}} + {V_{3}{h\left( {a,3,n,t,i} \right)}}}} & (37) \\{{\overset{\sim}{h}\left( {a,0,n,0,i} \right)} = {{V_{0}{h\left( {a,0,n,0,i} \right)}} + {V_{1}{h\left( {a,1,n,0,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,1,i} \right)}}} \right)}}} & (38) \\{{\overset{\sim}{h}\left( {a,0,n,1,i} \right)} = {{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,4,i} \right)}}} \right)} + {V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,4,i} \right)}}} \right)} + {V_{2}{h\left( {a,2,n,1,i} \right)}} + {V_{3}{h\left( {a,3,n,1,i} \right)}}}} & (39) \\{{\overset{\sim}{h}\left( {a,0,n,2,i} \right)} = {{V_{0}\left( {{\frac{1}{2}{h\left( {a,0,n,0,i} \right)}} + {\frac{1}{2}{h\left( {a,0,n,4,i} \right)}}} \right)} + {V_{1}\left( {{\frac{1}{2}{h\left( {a,1,n,0,i} \right)}} + {\frac{1}{2}{h\left( {a,1,n,4,i} \right)}}} \right)} + {V_{2}\left( {{\frac{6}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{1}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{6}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{1}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (40) \\{{\overset{\sim}{h}\left( {a,0,n,3,i} \right)} = {{V_{0}\left( {{\frac{1}{4}{h\left( {a,0,n,0,i} \right)}} + {\frac{3}{4}{h\left( {a,0,n,4,i} \right)}}} \right)} + {V_{1}\left( {{\frac{1}{4}{h\left( {a,1,n,0,i} \right)}} + {\frac{3}{4}{h\left( {a,1,n,4,i} \right)}}} \right)} + {V_{2}\left( {{\frac{5}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{2}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{5}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{2}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (41) \\{{\overset{\sim}{h}\left( {a,0,n,4,i} \right)} = {{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}{h\left( {a,1,n,4,i} \right)}} + {V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (42) \\{{\overset{\sim}{h}\left( {a,0,n,5,i} \right)} = {{V_{0}\left( {{\frac{2}{3}{h\left( {a,0,n,4,i} \right)}} + {\frac{1}{3}{h\left( {a,0,n,7,i} \right)}}} \right)} + {V_{1}\left( {{\frac{2}{3}{h\left( {a,1,n,4,i} \right)}} + {\frac{1}{3}{h\left( {a,1,n,7,i} \right)}}} \right)} + {V_{2}\left( {{\frac{3}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{4}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{3}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{4}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (43) \\{{\overset{\sim}{h}\left( {a,0,n,6,i} \right)} = {{V_{0}\left( {{\frac{1}{3}{h\left( {a,0,n,4,i} \right)}} + {\frac{2}{3}{h\left( {a,0,n,7,i} \right)}}} \right)} + {V_{1}\left( {{\frac{1}{3}{h\left( {a,1,n,4,i} \right)}} + {\frac{2}{3}{h\left( {a,1,n,7,i} \right)}}} \right)} + {V_{2}\left( {{\frac{2}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{5}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{2}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{5}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (44) \\{{\overset{\sim}{h}\left( {a,0,n,7,i} \right)} = {{V_{0}{h\left( {a,0,n,7,i} \right)}} + {V_{1}{h\left( {a,1,n,7,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (45) \\{{\overset{\sim}{h}\left( {a,0,n,8,i} \right)} = {{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,11,i} \right)}}} \right)} + {V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,11,i} \right)}}} \right)} + {V_{2}{h\left( {a,2,n,8,i} \right)}} + {V_{3}{h\left( {a,3,n,8,i} \right)}}}} & (46) \\{{\overset{\sim}{h}\left( {a,0,n,9,i} \right)} = {{V_{0}\left( {{\frac{1}{2}{h\left( {a,0,n,7,i} \right)}} + {\frac{1}{2}{h\left( {a,0,n,11,i} \right)}}} \right)} + {V_{1}\left( {{\frac{1}{2}{h\left( {a,1,n,7,i} \right)}} + {\frac{1}{2}{h\left( {a,1,n,11,i} \right)}}} \right)} + {V_{2}\left( {{\frac{6}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{1}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{6}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{1}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (47) \\{{\overset{\sim}{h}\left( {a,0,n,10,i} \right)} = {{V_{0}\left( {{\frac{1}{4}{h\left( {a,0,n,7,i} \right)}} + {\frac{3}{4}{h\left( {a,0,n,11,i} \right)}}} \right)} + {V_{1}\left( {{\frac{1}{4}{h\left( {a,1,n,7,i} \right)}} + {\frac{3}{4}{h\left( {a,1,n,11,i} \right)}}} \right)} + {V_{2}\left( {{\frac{5}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{2}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{5}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{2}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (48) \\{{\overset{\sim}{h}\left( {a,0,n,11,i} \right)} = {{V_{0}{h\left( {a,0,n,11,i} \right)}} + {V_{1}{h\left( {a,1,n,11,i} \right)}} + {V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{4}{7}{h\left( {a,3,{n + 1},8,i} \right)}} + {\frac{3}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (49) \\{{\overset{\sim}{h}\left( {a,0,n,12,i} \right)} = {{V_{0}\left( {{\frac{2}{3}{h\left( {a,0,n,11,i} \right)}} + {\frac{1}{3}{h\left( {a,0,{n + 1},0,i} \right)}}} \right)} + {V_{1}\left( {{\frac{2}{3}{h\left( {a,1,n,11,i} \right)}} + {\frac{1}{3}{h\left( {a,1,{n + 1},0,i} \right)}}} \right)} + {V_{2}\left( {{\frac{3}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{4}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{3}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{4}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (50) \\{{\overset{\sim}{h}\left( {a,0,n,13,i} \right)} = {{V_{0}\left( {{\frac{1}{3}{h\left( {a,0,n,11,i} \right)}} + {\frac{2}{3}{h\left( {a,0,{n + 1},0,i} \right)}}} \right)} + {V_{1}\left( {{\frac{1}{3}{h\left( {a,1,n,11,i} \right)}} + {\frac{2}{3}{h\left( {a,1,{n + 1},0,i} \right)}}} \right)} + {V_{2}\left( {{\frac{2}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{5}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{2}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{5}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (51)\end{matrix}$

Examples of the above-mentioned related art include Japanese Laid-openPatent Publication No. 2008-236428.

Incidentally, for the technology involving the above-mentioned channelestimation and de-precoding processes, the effective channel estimationvalues are calculated by obtaining the channel estimation values of allthe symbols and then performing de-precoding. Unfortunately, thisincreases the number of symbols to be interpolated in the time directionand the number of symbols to be de-precoded, increasing the complexity,followed by increases in power consumption.

SUMMARY

According to an aspect of the invention, a receiver includes a channelestimation unit that calculates channel estimation values of symbolscontaining pilot signals, from signals transmitted by a plurality ofantennas so to obtain channel estimation values of symbols in the samepositions of the antennas, a de-precoding unit that de-precodes thechannel estimation values of the antennas calculated by the channelestimation unit to calculate effective channel estimation values, and atime-direction interpolation unit that performs time-directioninterpolation using the effective channel estimation values calculatedby the de-precoding unit to calculate effective channel estimationvalues of symbols other than the symbols containing pilot signals.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the configuration of a receiver according to a firstembodiment;

FIG. 2 is a block diagram illustrating the configuration of a MIMO-OFDMsystem according to a second embodiment;

FIG. 3 is a block diagram illustrating the configuration of atransmitter according to the second embodiment;

FIG. 4 is a block diagram illustrating the configuration of a receiveraccording to the second embodiment;

FIG. 5 is a block diagram illustrating the detailed configuration of thechannel estimation unit of the receiver according to the secondembodiment;

FIG. 6 is a drawing illustrating time-direction interpolation andde-precoding;

FIG. 7 is a flowchart illustrating the process steps that the receiveraccording to the second embodiment performs;

FIG. 8 is a drawing illustrating time-direction interpolation andde-precoding;

FIG. 9 is a block diagram illustrating the detailed configuration of thereceiver; and

FIG. 10 is a drawing illustrating the related art.

DESCRIPTION OF EMBODIMENTS

Embodiments of a receiver, a communication system, and a channelestimation method according to the present invention will be describedin detail with reference to the accompanying drawings.

First, referring to FIG. 1, the configuration of a receiver according toa first embodiment will be described. FIG. 1 is a block diagramillustrating the configuration of the receiver according to the firstembodiment. As illustrated in FIG. 1, a receiver 1 includes a channelestimation unit 2, a de-precoding unit 3, a time-direction interpolationunit 4, a demodulator 5, and a decoder 6. The receiver 1 receivessignals transmitted by multiple transmitting antennas using a receivingantenna.

The channel estimation unit 2 calculates the channel estimation valuesof symbols containing pilot signals from the signals transmitted by thetransmitting antennas so that the channel estimation values of symbolsin the same positions of the antennas are obtained.

The de-precoding unit 3 de-precodes the channel estimation values of theantennas calculated by the channel estimation unit 2 so as to calculateeffective channel estimation values. The time-direction interpolationunit 4 performs linear interpolation in the time direction using theeffective channel estimation values calculated by the de-precoding unit3 so as to calculate the effective channel estimation values of symbolsother than the symbols containing pilot signals.

The demodulator 5 demodulates the transmitted signals using theeffective channel estimation values calculated by the time-directioninterpolation unit 4. The decoder 6 decodes the transmitted signalsdemodulated by the demodulator 5.

As seen, the receiver 1 obtains the channel estimation values of thesymbols in the same positions of the antennas, as well as calculates thechannel estimation values of the symbols containing pilot signals andde-precodes the latter channel estimation values. This may reduce thenumber of symbols to be interpolated in the time direction and thenumber of symbols to be de-precoded so as to reduce the complexity,resulting in reductions in power consumption to low levels.

Referring now to FIG. 2, the configuration of a MIMO-OFDM system will bedescribed. FIG. 2 is a block diagram illustrating the configuration of aMIMO-OFDM system according to a second embodiment. As illustrated, aMIMO-OFDM system 100 includes a receiver 10 provided with multiplereceiving antennas and a transmitter 20 provided with multipletransmitting antennas. The receiver 10 and transmitter 20 communicatewith each other wirelessly via multiple propagation paths.

The transmitter 20 transmits various signals to the receiver 10 usingthe multiple transmitting antennas. The signals transmitted by thetransmitter 20 are transmitted to the receiver 10 via the multiplepropagation paths. The transmitter 20 also assigns the subcarriers ofOFDM symbols to pieces of data to be transmitted to the receiver 10. Thereceiver 10 receives the signals and demodulates them on a subcarrierbasis to obtain each data.

Referring now to FIG. 3, the configuration of the transmitter 20 will bedescribed. FIG. 3 is a block diagram illustrating the configuration ofthe transmitter according to the second embodiment. As illustrated inFIG. 3, the transmitter 20 includes an encoder 21, a demodulator 22, alayer mapping unit 23, a precoding unit 24, Inverse Fast FourierTransform (IFFT) units 25, and Cyclic Prefix (CP) addition units 26. Theprocesses these components perform will be described below.

The encoder 21 encodes a bit sequence to be transmitted (e.g., turbocoding) and inputs the encoded bit sequence to the demodulator 22. Thedemodulator 22 modulates the encoded bit sequence into a transmissionsymbol (e.g., Quadrature Phase Sift Keying (QPSK), 16-State QuadratureAmplitude Modulation (16QAM)) and inputs the transmission symbol intothe layer mapping unit 23. The layer mapping unit 23 divides thedemodulated signal into multiple layers and inputs the layers into theprecoding unit 24.

The layers here refer to mutually independent signal sequences and aresubjected to precoding (to be discussed later) and then distributed tothe transmitting antennas. Precoding refers to that, in the case of,e.g., two layers and four transmitting antennas, the transmittergenerates four not independent signals from two independent signals by alinear operation and transmits the generated signals using the fourtransmitting antennas. In the above case, the receiver receives thesignals transmitted by the four transmitting antennas, but these signalsinclude only two independent ones actually.

The precoding unit 24 maps signals generated by combining the signals ofeach layer to the transmitting antennas. Specifically, the precodingunit 24 combines the signals of each layer by multiplying the signals bya precoding matrix (rows number=transmitting antennas number, columnsnumber=layers number) and maps the combined signals to the transmittingantennas. Such a precoding matrix is determined depending on the patternshared by the transmitter and receiver or the precoding matrix indicator(PMI) fed back by the receiver.

The IFFT units 25 corresponding to the transmitting antennas transformthe frequency-area signals into time-area signals by IFFT and outputsthe time-area signals. The CP addition units 26 corresponding to thetransmitting antennas add cyclic prefixes (CPs) to the time-areasignals. The resultant time-area signals are transmitted from themultiple transmitting antennas to the receiver 10.

Referring now to FIG. 4, the configuration of the receiver 10 will bedescribed. FIG. 4 is a block diagram illustrating the configuration ofthe receiver according to the second embodiment. As illustrated in FIG.4, the receiver 10 includes CP removal units 11, Fast Fourier Transform(FFT) units 12, a channel estimation unit 13, a PMI estimation unit 14,a de-precoding unit 15, a second time-direction interpolation unit 16, ademodulator 17, a layer mapping unit 18, and a decoder 19. The processesthese components perform will be described below.

The CP removal units 11 corresponding to the receiving antennas removethe CPs from the time-area signals and input the resultant time-areasignals into the FFT units 12. The FFT units 12 corresponding to thereceiving antennas transform the inputted time-area signals intofrequency-area signals by FFT and input the frequency-area signals intoboth the channel estimation unit 13 and demodulator 17.

The channel estimation unit 13 calculates the channel estimation valuesof symbols containing pilot signals from the signals transmitted by eachof a certain transmitting antenna. And also, the channel estimation unit13 linearly interpolates the channel estimation values of symbolscorresponding to the positions of symbols containing pilot signals fromthe signals transmitted by the other transmitting antennas so that thechannel estimation values of symbols in the same positions of theantennas are obtained.

The channel estimation value here refers to a value indicating a channelvariation between each transmitting antenna and each receiving antennaor a matrix where values indicating channel variations between eachtransmitting antenna and each receiving antenna are arranged.

Referring now to FIG. 5, the detailed configuration of the channelestimation unit 13 will be described. FIG. 5 is a block diagramillustrating the detailed configuration of the channel estimation unitof the receiver according to the second embodiment. As illustrated inFIG. 5, the channel estimation unit 13 includes a frequency-directioninterpolation unit 13 a, a first time-direction interpolation unit 13 b,and a pilot position channel estimation unit 13 c.

The pilot position channel estimation unit 13 c obtains the channelestimation values of resource elements where pilot signals are arranged.The frequency-direction interpolation unit 13 a then performs linearinterpolation in the frequency direction using the channel estimationvalues of the resource elements where pilot signals are arranged so asto obtain the channel estimation values of all the resource elements inOFDM symbols and inputs the obtained channel estimation values into thefirst time-direction interpolation unit 13 b.

The first time-direction interpolation unit 13 b performs linearinterpolation in the time direction using the channel estimation valuesof the OFDM symbols where pilot signals are arranged. Specifically, thefirst time-direction interpolation unit 13 b performs time-directioninterpolation using the channel estimation values of the OFDM symbolscontaining pilot signals, of the transmitted signals.

The above process will be described specifically using the exampleillustrated in FIG. 6. For example, the transmitter 20 is provided withfour antennas having the transmitting antenna numbers 0 to 3. Asillustrated in FIG. 6, with regard to the signals having thetransmitting antenna numbers 0 and 1 (TxAnt#0, 1 in FIG. 6) of thosetransmitted by the above-mentioned transmitting antennas, pilot signalsare arranged in the OFDM symbols having the symbol numbers 0, 4, 7, and11. On the other hand, with regard to the signals transmitted by thetransmitting antennas having the transmitting antenna numbers 2 and 3(TxAnt#2, 3 in FIG. 6), pilot signals are arranged in the OFDM symbolshaving the symbol numbers 1 and 8.

In such a case, as indicated by Formula (1) below, the pilot positionchannel estimation unit 13 c and frequency-direction interpolation unit13 a obtain the channel estimation values of the OFDM symbols having thesymbol numbers 0, 4, 7, and 11 from the signals transmitted by thetransmitting antennas having the transmitting antenna numbers 0 and 1.The first time-direction interpolation unit 13 b then performstime-direction interpolation using the channel estimation values of theOFDM symbols having the symbol numbers 0, 4, 7, and 11 so as to obtainthe channel estimation values of the OFDM symbols having the symbolnumbers 1 and 8, as indicated by Formula (1) below.

$\begin{matrix}{{h\left( {a,b,n,t,i} \right)} = \left\{ \begin{matrix}{h\left( {a,b,n,0,i} \right)} & \left( {{b = 0},1,{t = 0}} \right) \\{{\frac{3}{4}{h\left( {a,b,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,b,n,4,i} \right)}}} & \left( {{b = 0},1,{t = 1}} \right) \\{h\left( {a,b,n,4,i} \right)} & \left( {{b = 0},1,{t = 4}} \right) \\{h\left( {a,b,n,7,i} \right)} & \left( {{b = 0},1,{t = 7}} \right) \\{{\frac{3}{4}{h\left( {a,b,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,b,n,11,i} \right)}}} & \left( {{b = 0},1,{t = 8}} \right) \\{h\left( {a,b,n,11,i} \right)} & \left( {{b = 0},1,{t = 11}} \right)\end{matrix} \right.} & (1)\end{matrix}$

Also, as indicated by Formula (2) below, the pilot position channelestimation unit 13 c and frequency-direction interpolation unit 13 aobtain the channel estimation values of the OFDM symbols having thesymbol numbers 1 and 8 of the signals transmitted by the transmittingantennas having the transmitting antenna numbers 2 and 3. The firsttime-direction interpolation unit 13 b then performs time-directioninterpolation using the channel estimation values of the OFDM symbolshaving the symbol numbers 1 and 8 so as to obtain the channel estimationvalues of the OFDM symbols having the symbol numbers 0, 4, 7, and 11, asindicated by Formula (2). The obtained channel estimation values of theOFDM symbols having the symbol numbers 0, 1, 4, 7, 8, and 11 of all thetransmitting antennas are inputted into the PMI estimation unit 14 andde-precoding unit 15.

$\begin{matrix}{{h\left( {a,b,n,t,i} \right)} = \left\{ \begin{matrix}{{\frac{1}{7}{h\left( {a,b,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,b,n,1,i} \right)}}} & \left( {{b = 2},3,{t = 0}} \right) \\{h\left( {a,b,n,1,i} \right)} & \left( {{b = 2},3,{t = 1}} \right) \\{{\frac{4}{7}{h\left( {a,b,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,b,n,8,i} \right)}}} & \left( {{b = 2},3,{t = 4}} \right) \\{{\frac{1}{7}{h\left( {a,b,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,b,n,8,i} \right)}}} & \left( {{b = 2},3,{t = 7}} \right) \\{h\left( {a,b,n,8,i} \right)} & \left( {{b = 2},3,{t = 8}} \right) \\{{\frac{4}{7}{h\left( {a,b,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,b,{n + 1},1,i} \right)}}} & \left( {{b = 2},3,{t = 11}} \right)\end{matrix} \right.} & (2)\end{matrix}$

The PMI estimation unit 14 selects an optimum PMI from the channelestimation values and feeds back the optimum PMI to the transmitter 20.The de-precoding unit 15 de-precodes the channel estimation values ofthe antennas to calculate effective channel estimation values. Theeffective channel estimation value here refers to a value indicating achannel variation between each layer and each receiving antenna. Aneffective channel estimation value matrix where the effective channelestimation values between each layer and each receiving antenna arearranged is obtained by multiplying a channel estimation value matrixwhere channel estimation values between each transmitting antenna andeach receiving antenna are arranged by a precoding matrix.

The precoding matrix to be used in the multiplication is determineddepending on the pattern shared by the transmitter and receiver or thePMI previously fed back to the transmitter 20.

The above process will be described with reference to FIG. 6. Asindicated by Formulas (3) to (8) below, the de-precoding unit 15de-precodes the channel estimation values of the OFDM symbols having thesymbol numbers 0, 1, 4, 7, 8, and 11 calculated by the firsttime-direction interpolation unit 13 b so as to calculate the effectivechannel estimation values. The de-precoding unit 15 then inputs theobtained effective channel estimation values of the OFDM symbols havingthe symbol numbers 0, 1, 4, 7, 8, and 11 into the second time-directioninterpolation unit 16.

$\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,0,i} \right)} = {{V_{0}{h\left( {a,0,n,0,i} \right)}} + {V_{1}{h\left( {a,1,n,0,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,1,i} \right)}}} \right)}}} & (3) \\{{\overset{\sim}{h}\left( {a,0,n,1,i} \right)} = {{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,4,i} \right)}}} \right)} + {V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,4,i} \right)}}} \right)} + {V_{2}{h\left( {a,2,n,1,i} \right)}} + {V_{3}{h\left( {a,3,n,1,i} \right)}}}} & (4) \\{{\overset{\sim}{h}\left( {a,0,n,4,i} \right)} = {{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}{h\left( {a,1,n,4,i} \right)}} + {V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (5) \\{{\overset{\sim}{h}\left( {a,0,n,7,i} \right)} = {{V_{0}{h\left( {a,0,n,7,i} \right)}} + {V_{1}{h\left( {a,1,n,7,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (6) \\{{\overset{\sim}{h}\left( {a,0,n,8,i} \right)} = {{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,11,i} \right)}}} \right)} + {V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,11,i} \right)}}} \right)} + {V_{2}{h\left( {a,2,n,8,i} \right)}} + {V_{3}{h\left( {a,3,n,8,i} \right)}}}} & (7) \\{{\overset{\sim}{h}\left( {a,0,n,11,i} \right)} = {{V_{0}{h\left( {a,0,n,11,i} \right)}} + {V_{1}{h\left( {a,1,n,11,i} \right)}} + {V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{4}{7}{h\left( {a,3,{n + 1},8,i} \right)}} + {\frac{3}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (8)\end{matrix}$

The second time-direction interpolation unit 16 performs linearinterpolation in the time direction using the effective channelestimation values so as to calculate effective channel estimation valuesof symbols other than the symbols containing pilot signals. This will bedescribed with reference to FIG. 6. The second time-directioninterpolation unit 16 performs linear interpolation in the timedirection using the effective channel estimation values of the OFDMsymbols having the symbol numbers 0, 1, 4, 7, 8, and 11 so as tocalculate the effective channel estimation values of the OFDM symbolshaving the symbol numbers 2, 3, 5, 6, 9, and 10.

Here, in order to obtain the effective channel estimation values of theOFDM symbols having the symbol numbers 12 and 13, the secondtime-direction interpolation unit 16 requires the effective channelestimation value of the OFDM symbol having the symbol number 0 of thesubsequent sub-frame. Specifically, the same precoding method needs tohave been applied to two symbols (in this example, the symbol having thesymbol number 11 and the symbol having the symbol number 0 of thesubsequent sub-frame) to be used in time-direction linear interpolation.Different precoding, however, may have been applied to the subsequentsub-frame, so linear interpolation cannot be simply performed.

For this reason, as indicated by Formula (9) below, the secondtime-direction interpolation unit 16 de-precodes the channel estimationvalue of the symbol having the symbol number 0 of the subsequentsub-frame using the precoding method applied to the current sub-frame soas to obtain the effective channel estimation value.

$\begin{matrix}{{\overset{\sim}{h}\left( {a,0,{n + 1},0,i} \right)} = {{V_{0}{h\left( {a,0,{n + 1},0,i} \right)}} + {V_{1}{h\left( {a,1,{n + 1},0,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (9)\end{matrix}$

Then, as indicated by Formulas (10) to (15) below, the secondtime-direction interpolation unit 16 calculates the effective channelestimation values of the OFDM symbols having the symbol numbers 2, 3, 5,6, 9, and 10 using the effective channel estimation values of the OFDMsymbols having the symbol numbers 0, 1, 4, 7, 8, and 11.

$\begin{matrix}\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,2,i} \right)} = {{\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,1,i} \right)}} + {\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}}}} \\{= {{\frac{2}{3}\begin{pmatrix}{{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,4,i} \right)}}} \right)} +} \\{{V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,4,i} \right)}}} \right)} +} \\{{V_{2}{h\left( {a,2,n,1,i} \right)}} + {V_{3}{h\left( {a,3,n,1,i} \right)}}}\end{pmatrix}} +}} \\{{\frac{1}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}h\left( {a,1,n,4,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{1}{2}{h\left( {a,0,n,0,i} \right)}} + {\frac{1}{2}{h\left( {a,0,n,4,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{2}{h\left( {a,1,n,0,i} \right)}} + {\frac{1}{2}{h\left( {a,1,n,4,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{6}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{1}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{6}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{1}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}\end{matrix} & (10) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,3,i} \right)} = {{\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,1,i} \right)}} + {\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{4}{h\left( {a,0,n,0,i} \right)}} + {\frac{3}{4}{h\left( {a,0,n,4,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{4}{h\left( {a,1,n,0,i} \right)}} + {\frac{3}{4}{h\left( {a,1,n,4,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{5}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{2}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{5}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{2}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}\end{matrix} & (11) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,5,i} \right)} = {{\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}} + {\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}}}} \\{= {{\frac{2}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}h\left( {a,1,n,4,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}\end{pmatrix}} +}} \\{{\frac{1}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,7,i} \right)}} + {V_{1}h\left( {a,1,n,7,i} \right)} +} \\{{V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{2}{3}{h\left( {a,0,n,4,i} \right)}} + {\frac{1}{3}{h\left( {a,0,n,7,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{2}{3}{h\left( {a,1,n,4,i} \right)}} + {\frac{1}{3}{h\left( {a,1,n,7,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{3}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{4}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{3}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{4}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}\end{matrix} & (12) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,6,i} \right)} = {{\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}} + {\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{3}{h\left( {a,0,n,4,i} \right)}} + {\frac{2}{3}{h\left( {a,0,n,7,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{3}{h\left( {a,1,n,4,i} \right)}} + {\frac{2}{3}{h\left( {a,1,n,7,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{2}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{5}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{2}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{5}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}\end{matrix} & (13) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,9,i} \right)} = {{\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,8,i} \right)}} + {\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}}}} \\{= {{\frac{2}{3}\begin{pmatrix}{{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,11,i} \right)}}} \right)} +} \\{{V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,11,i} \right)}}} \right)} +} \\{{V_{2}{h\left( {a,2,n,8,i} \right)}} + {V_{3}{h\left( {a,3,n,8,i} \right)}}}\end{pmatrix}} +}} \\{{\frac{1}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,11,i} \right)}} + {V_{1}h\left( {a,1,n,11,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{1}{2}{h\left( {a,0,n,7,i} \right)}} + {\frac{1}{2}{h\left( {a,0,n,11,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{2}{h\left( {a,1,n,7,i} \right)}} + {\frac{1}{2}{h\left( {a,1,n,11,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{6}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{1}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{6}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{1}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}\end{matrix} & (14) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,10,i} \right)} = {{\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}} + {\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{4}{h\left( {a,0,n,7,i} \right)}} + {\frac{3}{4}{h\left( {a,0,n,11,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{4}{h\left( {a,1,n,7,i} \right)}} + {\frac{3}{4}{h\left( {a,1,n,11,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{5}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{2}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{5}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{2}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}\end{matrix} & (15)\end{matrix}$

Then, as indicated by Formulas (16) to (17) below, the secondtime-direction interpolation unit 16 calculates the effective channelestimation values of the OFDM symbols having the symbol numbers 12 and13 using the effective channel estimation value of the OFDM symbolhaving the symbol number 11 and that of the OFDM symbol having thesymbol number 0 of the subsequent sub-frame obtained by Formula (9). Thesecond time-direction interpolation unit 16 then inputs the calculatedeffective channel estimation values into the demodulator 17.

$\begin{matrix}\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,12,i} \right)} = {{\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}} + {\frac{1}{3}{\overset{\sim}{h}\left( {a,0,{n + 1},0,i} \right)}}}} \\{= {{\frac{2}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,11,i} \right)}} + {V_{1}h\left( {a,1,n,11,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}\end{pmatrix}} +}} \\{{\frac{1}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,{n + 1},0,i} \right)}} + {V_{1}h\left( {a,1,{n + 1},0,i} \right)} +} \\{{V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{2}{3}{h\left( {a,0,n,11,i} \right)}} + {\frac{1}{3}{h\left( {a,0,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{2}{3}{h\left( {a,1,n,11,i} \right)}} + {\frac{1}{3}{h\left( {a,1,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{3}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{4}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{3}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{4}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}\end{matrix} & (16) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,13,i} \right)} = {{\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}} + {\frac{2}{3}{\overset{\sim}{h}\left( {a,0,{n + 1},0,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{3}{h\left( {a,0,n,11,i} \right)}} + {\frac{2}{3}{h\left( {a,0,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{3}{h\left( {a,1,n,11,i} \right)}} + {\frac{2}{3}{h\left( {a,1,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{2}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{5}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{2}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{5}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}\end{matrix} & (17)\end{matrix}$

The demodulator 17 performs demodulation using the effective channelestimation values. Specifically, the demodulator 17 removes channelvariations or noise relating to the received symbols using the effectivechannel estimation values, converts the resultant received symbols intolayer-specific log-likelihood ratios, and inputs the log-likelihoodratios into the layer mapping unit 18.

The layer mapping unit 18 converts the layer-specific log-likelihoodratios obtained by the demodulator 17 into sequences to be inputted tothe decoding unit 19. The decoder 19 cancels the encoding performed bythe transmitter 20 to correct errors.

Referring now to FIG. 7, the process the receiver 10 according to thesecond embodiment performs will be described. FIG. 7 is a flowchartillustrating the process the receiver 10 according to the secondembodiment performs.

As illustrated in FIG. 7, the channel estimation unit 13 of the receiver10 obtains the channel estimation values of the OFDM symbols where pilotsignals are arranged (step S101) with respect to the signals transmittedby the transmitting antennas and performs linear interpolation in thefrequency direction using the obtained channel estimation values (stepS102).

The channel estimation unit 13 then performs time-directioninterpolation using the channel estimation values of the OFDM symbolscontaining pilot signals so as to obtain the channel estimation valuesof OFDM symbols other than the OFDM symbols containing pilot signals(step S103). The de-precoding unit 15 then de-precodes the OFDM symbolswhose channel estimation value has been obtained so as to obtaineffective channel estimation values (step S104).

The second time-direction interpolation unit 16 then performstime-direction interpolation using the calculated effective channelestimation values (step S105). The demodulator 17 then performsdemodulation using the effective channel estimation values (step S106).The layer mapping unit 18 then converts the layer-specificlog-likelihood ratios into sequences to be inputted to the decoder 19(step S107). Subsequently, the decoder 19 performs decoding and thencorrect errors (step S108), completing the process.

As described above, the receiver 10 calculates the channel estimationvalues of symbols containing pilot signals, from the signals transmittedby the transmitting antennas so that the channel estimation values ofsymbols in the same positions of the antennas are obtained. The receiver10 then de-precodes the calculated channel estimation values of eachantenna so as to calculate effective channel estimation values. Usingthe calculated effective channel estimation values, the receiver 10performs time-direction interpolation to calculate the effective channelestimation values of symbols other than the symbols containing pilotsignals. This may reduce the number of symbols to be interpolated in thetime direction and the number of symbols to be de-precoded so as toreduce the complexity, resulting in reductions in power consumption tolow levels.

Also, according to the second embodiment, the receiver 10 calculates thechannel estimation values of the symbols containing pilot signals fromthe signals transmitted by the antennas. Then, in the signal transmittedby each antenna, the receiver 10 linearly interpolates the channelestimation values of symbols corresponding to the positions of thesymbols containing pilot signals from the signals transmitted by theother antennas so that the channel estimation values of the symbols inthe same positions among the antennas are obtained. This may reduce thenumber of symbols to be interpolated in the time direction and thenumber of symbols to be de-precoded so as to reduce the complexity,resulting in reductions in power consumption to low levels.

In the second embodiment, the case has been described where, in thesignal transmitted by each transmitting antenna, the channel estimationvalues of symbols where pilots are arranged in the other transmittingantennas are obtained; the channel estimation values of the same symbolsamong the transmitting antennas are obtained; and then de-precoding isperformed. However, this embodiment is not limited thereto. It is alsopossible to obtain the channel estimation values of symbolscorresponding to the positions of symbols containing pilot signals fromthe signal transmitted by one of the multiple transmitting antennas andthen to perform de-precoding.

Hereafter, the process that a receiver according to the third embodimentperforms will be described with reference to FIG. 8, where the channelestimation values of symbols where pilots are arranged, of one of thesignals transmitted by the transmitting antennas are obtained and thende-precoding is performed. The configuration of the receiver is the sameas that of the receiver according to the second embodiment and will notbe described.

FIG. 8 is a drawing illustrating time-direction interpolation andde-precoding. In an example illustrated in FIG. 8, as for the signalstransmitted by the transmitting antennas having the transmitting antennanumbers 0 and 1 (TxAnt#0, 1 in FIG. 8) of the above-mentionedtransmitting antennas, pilot signals are arranged in the symbols havingthe symbol numbers 0, 4, 7, and 11. As for signals transmitted by thetransmitting antennas having the transmitting antenna numbers 2 and 3(TxAnt#2, 3 in FIG. 8), pilot signals are arranged in the symbols havingthe symbol numbers 1 and 8.

As illustrated in FIG. 8, with respect to the signals transmitted by thetransmitting antennas having the transmitting antenna numbers 0 and 1,the receiver according to the third embodiment obtains the channelestimation values of the OFDM symbols having the symbol numbers 0, 4, 7,and 11, as indicated by Formula (18) below.

$\begin{matrix}{{h\left( {a,b,n,t,i} \right)} = \left\{ \begin{matrix}{h\left( {a,b,n,0,i} \right)} & \left( {{b = 0},1,{t = 0}} \right) \\{h\left( {a,b,n,4,i} \right)} & \left( {{b = 0},1,{t = 4}} \right) \\{h\left( {a,b,n,7,i} \right)} & \left( {{b = 0},1,{t = 7}} \right) \\{h\left( {a,b,n,11,i} \right)} & \left( {{b = 0},1,{t = 11}} \right)\end{matrix} \right.} & (18)\end{matrix}$

With respect to the signals transmitted by the transmitting antennashaving the transmitting antenna numbers 2 and 3, the receiver obtainsthe channel estimation values of the OFDM symbols having the symbolnumbers 1 and 8, as indicated by Formula (19) below. The receiver thenperforms time-direction interpolation using the channel estimationvalues of the OFDM symbols having the symbol numbers 1 and 8 so as toobtain the channel estimation values of the OFDM symbols having thesymbol numbers 0, 4, 7, and 11, as indicated by Formula (19). Thus, thereceiver obtains the channel estimation values of the OFDM symbolshaving the symbol numbers 0, 4, 7, and 11 with respect to all thetransmitting antennas.

$\begin{matrix}{{h\left( {a,b,n,t,i} \right)} = \left\{ \begin{matrix}{{\frac{1}{7}{h\left( {a,b,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,b,n,1,i} \right)}}} & \left( {{b = 2},3,{t = 0}} \right) \\{h\left( {a,b,n,1,i} \right)} & \left( {{b = 2},3,{t = 1}} \right) \\{{\frac{4}{7}{h\left( {a,b,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,b,n,8,i} \right)}}} & \left( {{b = 2},3,{t = 4}} \right) \\{{\frac{1}{7}{h\left( {a,b,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,b,n,8,i} \right)}}} & \left( {{b = 2},3,{t = 7}} \right) \\{h\left( {a,b,n,8,i} \right)} & \left( {{b = 2},3,{t = 8}} \right) \\{{\frac{4}{7}{h\left( {a,b,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,b,{n + 1},1,i} \right)}}} & \left( {{b = 2},3,{t = 11}} \right)\end{matrix} \right.} & (19)\end{matrix}$

Then, as indicated by Formulas (20) to (23) below, the receiver precodesthe calculated channel estimation values of the OFDM symbols having thesymbol numbers 0, 4, 7, and 11 so as to calculate the effective channelestimation values of these OFDM symbols.

$\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,0,i} \right)} = {{V_{0}{h\left( {a,0,n,0,i} \right)}} + {V_{1}{h\left( {a,1,n,0,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,1,i} \right)}}} \right)}}} & (20) \\{{\overset{\sim}{h}\left( {a,0,n,4,i} \right)} = {{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}{h\left( {a,1,n,4,i} \right)}} + {V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (21) \\{{\overset{\sim}{h}\left( {a,0,n,7,i} \right)} = {{V_{0}{h\left( {a,0,n,7,i} \right)}} + {V_{1}{h\left( {a,1,n,7,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}} & (22) \\{{\overset{\sim}{h}\left( {a,0,n,11,i} \right)} = {{V_{0}{h\left( {a,0,n,11,i} \right)}} + {V_{1}{h\left( {a,1,n,11,i} \right)}} + {V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{4}{7}{h\left( {a,3,{n + 1},8,i} \right)}} + {\frac{3}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (23)\end{matrix}$

The receiver then performs time-direction linear interpolation using theeffective channel estimation values of the OFDM symbols having thesymbol numbers 0, 4, 7, and 11 so as to calculate the effective channelestimation values of the OFDM symbols having the symbol numbers 1, 2, 3,5, 6, 8, 9, and 10.

In this case, as in the second embodiment, the receiver de-precodes thechannel estimation value of the symbol having the symbol number 0 of thesubsequent sub-frame using the precoding method applied to the currentsub-frame so as to obtain the effective channel estimation values, asindicated by Formula (24) below.

$\begin{matrix}{{\overset{\sim}{h}\left( {a,0,{n + 1},0,i} \right)} = {{V_{0}{h\left( {a,0,{n + 1},0,i} \right)}} + {V_{1}{h\left( {a,1,{n + 1},0,i} \right)}} + {V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} + {V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}} & (24)\end{matrix}$

The receiver then calculates the effective channel estimation values ofthe OFDM symbols having symbol numbers 1, 2, 3, 5, 6, 8, 9, and 10 usingthose of the OFDM symbols having the symbol numbers 0, 4, 7, and 11, asindicated by Formulas (25) to (32) below.

$\begin{matrix}\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,1,i} \right)} = {{\frac{3}{4}{\overset{\sim}{h}\left( {a,0,n,0,i} \right)}} + {\frac{1}{4}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}}}} \\{= {{\frac{3}{4}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,0,i} \right)}} + {V_{1}h\left( {a,1,n,0,i} \right)} +} \\{{V_{2}\left( {{\frac{1}{7}{h\left( {a,2,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,1,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{1}{7}{h\left( {a,3,{n - 1},8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,1,i} \right)}}} \right)}\end{pmatrix}} +}} \\{{\frac{1}{4}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}h\left( {a,1,n,4,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,4,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,0,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,4,i} \right)}}} \right)} +}} \\{{{V_{2}\begin{pmatrix}{{\frac{3}{28}h\left( {a,2,{n - 1},8,i} \right)} + {\frac{11}{14}{h\left( {a,2,n,1,i} \right)}} +} \\{\frac{3}{28}{h\left( {a,2,n,8,i} \right)}}\end{pmatrix}} +}} \\{{V_{3}\begin{pmatrix}{{\frac{3}{28}h\left( {a,3,{n - 1},8,i} \right)} + {\frac{11}{14}{h\left( {a,3,n,1,i} \right)}} +} \\{\frac{3}{28}{h\left( {a,3,n,8,i} \right)}}\end{pmatrix}}}\end{matrix} & (25) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,2,i} \right)} = {{\frac{1}{2}{\overset{\sim}{h}\left( {a,0,n,0,i} \right)}} + {\frac{1}{2}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{2}{h\left( {a,0,n,0,i} \right)}} + {\frac{1}{2}{h\left( {a,0,n,4,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{2}{h\left( {a,1,n,0,i} \right)}} + {\frac{1}{2}{h\left( {a,1,n,4,i} \right)}}} \right)} +}} \\{{{V_{2}\begin{pmatrix}{{\frac{1}{14}{h\left( {a,2,{n - 1},8,i} \right)}} + {\frac{5}{7}h\left( {a,2,n,1,i} \right)} +} \\{\frac{3}{14}{h\left( {a,2,n,8,i} \right)}}\end{pmatrix}} +}} \\{{V_{3}\begin{pmatrix}{{\frac{1}{14}{h\left( {a,3,{n - 1},8,i} \right)}} + {\frac{5}{7}h\left( {a,3,n,1,i} \right)} +} \\{\frac{3}{14}{h\left( {a,3,n,8,i} \right)}}\end{pmatrix}}}\end{matrix} & (26) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,3,i} \right)} = {{\frac{1}{4}{\overset{\sim}{h}\left( {a,0,n,0,i} \right)}} + {\frac{3}{4}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{4}{h\left( {a,0,n,0,i} \right)}} + {\frac{3}{4}{h\left( {a,0,n,4,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{4}{h\left( {a,1,n,0,i} \right)}} + {\frac{3}{4}{h\left( {a,1,n,4,i} \right)}}} \right)} +}} \\{{{V_{2}\begin{pmatrix}{{\frac{1}{28}{h\left( {a,2,{n - 1},8,i} \right)}} + {\frac{9}{14}h\left( {a,2,n,1,i} \right)} +} \\{\frac{9}{28}{h\left( {a,2,n,8,i} \right)}}\end{pmatrix}} +}} \\{{V_{3}\begin{pmatrix}{{\frac{1}{28}{h\left( {a,3,{n - 1},8,i} \right)}} + {\frac{9}{14}h\left( {a,3,n,1,i} \right)} +} \\{\frac{9}{28}{h\left( {a,3,n,8,i} \right)}}\end{pmatrix}}}\end{matrix} & (27) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,5,i} \right)} = {{\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}} + {\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}}}} \\{= {{\frac{2}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}h\left( {a,1,n,4,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{3}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}\end{pmatrix}} +}} \\{{\frac{1}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,7,i} \right)}} + {V_{1}h\left( {a,1,n,7,i} \right)} +} \\{{V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{2}{3}{h\left( {a,0,n,4,i} \right)}} + {\frac{1}{3}{h\left( {a,0,n,7,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{2}{3}{h\left( {a,1,n,4,i} \right)}} + {\frac{1}{3}{h\left( {a,1,n,7,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{3}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{4}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{3}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{4}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}\end{matrix} & (28) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,6,i} \right)} = {{\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,4,i} \right)}} + {\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{3}{h\left( {a,0,n,4,i} \right)}} + {\frac{2}{3}{h\left( {a,0,n,7,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{3}{h\left( {a,1,n,4,i} \right)}} + {\frac{2}{3}{h\left( {a,1,n,7,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{2}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{5}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{2}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{5}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}}\end{matrix} & (29) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,8,i} \right)} = {{\frac{3}{4}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}} + {\frac{1}{4}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}}}} \\{= {{\frac{3}{4}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,7,i} \right)}} + {V_{1}h\left( {a,1,n,7,i} \right)} +} \\{{V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,2,n,8,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,1,i} \right)}} + {\frac{6}{7}{h\left( {a,3,n,8,i} \right)}}} \right)}\end{pmatrix}} +}} \\{{\frac{1}{4}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,11,i} \right)}} + {V_{1}h\left( {a,1,n,11,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{3}{4}{h\left( {a,0,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,0,n,11,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{3}{4}{h\left( {a,1,n,7,i} \right)}} + {\frac{1}{4}{h\left( {a,1,n,11,i} \right)}}} \right)} +}} \\{{{V_{2}\begin{pmatrix}{{\frac{3}{28}{h\left( {a,2,n,1,i} \right)}} + {\frac{11}{14}h\left( {a,2,n,8,i} \right)} +} \\{\frac{3}{28}{h\left( {a,2,{n + 1},1,i} \right)}}\end{pmatrix}} +}} \\{{V_{3}\begin{pmatrix}{{\frac{3}{28}{h\left( {a,3,n,1,i} \right)}} + {\frac{11}{14}h\left( {a,3,n,8,i} \right)} +} \\{\frac{3}{28}{h\left( {a,3,{n + 1},11,i} \right)}}\end{pmatrix}}}\end{matrix} & (30) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,9,i} \right)} = {{\frac{1}{2}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}} + {\frac{1}{2}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{2}{h\left( {a,0,n,7,i} \right)}} + {\frac{1}{2}{h\left( {a,0,n,11,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{2}{h\left( {a,1,n,7,i} \right)}} + {\frac{1}{2}{h\left( {a,1,n,11,i} \right)}}} \right)} +}} \\{{{V_{2}\begin{pmatrix}{{\frac{1}{14}{h\left( {a,2,n,1,i} \right)}} + {\frac{5}{7}h\left( {a,2,n,8,i} \right)} +} \\{\frac{3}{14}{h\left( {a,2,{n + 1},1,i} \right)}}\end{pmatrix}} +}} \\{{V_{3}\begin{pmatrix}{{\frac{1}{14}{h\left( {a,3,n,1,i} \right)}} + {\frac{5}{7}h\left( {a,3,n,8,i} \right)} +} \\{\frac{3}{14}{h\left( {a,3,{n + 1},1,i} \right)}}\end{pmatrix}}}\end{matrix} & (31) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,10,i} \right)} = {{\frac{1}{4}{\overset{\sim}{h}\left( {a,0,n,7,i} \right)}} + {\frac{3}{4}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{4}{h\left( {a,0,n,7,i} \right)}} + {\frac{3}{4}{h\left( {a,0,n,11,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{4}{h\left( {a,1,n,7,i} \right)}} + {\frac{3}{4}{h\left( {a,1,n,11,i} \right)}}} \right)} +}} \\{{{V_{2}\begin{pmatrix}{{\frac{1}{28}{h\left( {a,2,n,1,i} \right)}} + {\frac{9}{14}h\left( {a,2,n,8,i} \right)} +} \\{\frac{9}{28}{h\left( {a,2,{n + 1},1,i} \right)}}\end{pmatrix}} +}} \\{{V_{3}\begin{pmatrix}{{\frac{1}{28}{h\left( {a,3,n,1,i} \right)}} + {\frac{9}{14}h\left( {a,3,n,8,i} \right)} +} \\{\frac{9}{28}{h\left( {a,3,{n + 1},1,i} \right)}}\end{pmatrix}}}\end{matrix} & (32)\end{matrix}$

The receiver then calculates the effective channel estimation values ofthe OFDM symbols having the symbol numbers 12 and 13 using that of theOFDM symbol having the symbol number 11, as indicated by Formulas (33)to (34) below. The receiver then performs demodulation and decoding.

$\begin{matrix}\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,12,i} \right)} = {{\frac{2}{3}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}} + {\frac{1}{3}{\overset{\sim}{h}\left( {a,0,{n + 1},0,i} \right)}}}} \\{= {{\frac{2}{3}\begin{pmatrix}{{V_{0}{h\left( {a,7,n,4,i} \right)}} + {V_{1}h\left( {a,1,n,11,i} \right)} +} \\{{V_{2}\left( {{\frac{4}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{4}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{3}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}\end{pmatrix}} +}} \\{{\frac{1}{3}\begin{pmatrix}{{V_{0}{h\left( {a,0,n,4,i} \right)}} + {V_{1}h\left( {a,1,n,11,i} \right)} +} \\{{V_{2}\left( {{\frac{1}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +} \\{V_{3}\left( {{\frac{1}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{6}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}\end{pmatrix}}} \\{= {{V_{0}\left( {{\frac{2}{3}{h\left( {a,0,n,11,i} \right)}} + {\frac{1}{3}{h\left( {a,0,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{2}{3}{h\left( {a,1,n,11,i} \right)}} + {\frac{1}{3}{h\left( {a,1,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{3}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{4}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{3}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{4}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}\end{matrix} & (33) \\\begin{matrix}{{\overset{\sim}{h}\left( {a,0,n,13,i} \right)} = {{\frac{1}{3}{\overset{\sim}{h}\left( {a,0,n,11,i} \right)}} + {\frac{2}{3}{\overset{\sim}{h}\left( {a,0,{n + 1},0,i} \right)}}}} \\{= {{V_{0}\left( {{\frac{1}{3}{h\left( {a,0,n,11,i} \right)}} + {\frac{2}{3}{h\left( {a,0,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{1}\left( {{\frac{1}{3}{h\left( {a,1,n,11,i} \right)}} + {\frac{2}{3}{h\left( {a,1,{n + 1},0,i} \right)}}} \right)} +}} \\{{{V_{2}\left( {{\frac{2}{7}{h\left( {a,2,n,8,i} \right)}} + {\frac{5}{7}{h\left( {a,2,{n + 1},1,i} \right)}}} \right)} +}} \\{{V_{3}\left( {{\frac{2}{7}{h\left( {a,3,n,8,i} \right)}} + {\frac{5}{7}{h\left( {a,3,{n + 1},1,i} \right)}}} \right)}}\end{matrix} & (34)\end{matrix}$

As seen, in the third embodiment, the channel estimation values of thesymbols containing pilot signals from the signals transmitted by theantennas are calculated. Then, the channel estimation values of symbolscorresponding to the positions of the symbols containing pilot signalsfrom the signal transmitted by one of the antennas are linearlyinterpolated. This can further reduce the number of symbols to beinterpolated in the time direction and the number of symbols to bede-precoded so as to further reduce the complexity, resulting inreductions in power consumption to lower levels.

While the first to third embodiments have been described, the presentinvention may be carried out as various embodiments other than theseembodiments. Hereafter, another embodiment included in the presentinvention as a fourth embodiment will be described.

In the above-mentioned third embodiment, the case has been describedwhere the channel estimation values of symbols corresponding to thepositions of the symbols containing pilot signals from the signaltransmitted by one of the antennas are obtained so that the channelestimation values having the same symbol numbers of the antennas areobtained. However, the present invention is not limited thereto. One ofthe multiple antennas may be selected according to the arrangementintervals of pilot signals in the signals transmitted by the antennas,and the positions of symbols to be de-precoded of each antenna may bematched with the positions of the symbols containing pilot signals, ofthe selected antenna.

For example, in a case where the receiver selects an antenna where pilotsignals are arranged at large intervals and the positions of symbols tobe de-precoded are matched with one another among the antennas, thecomplexity may be further reduced. In contrast, in a case where thereceiver selects an antenna where pilot signals are arranged at smallintervals and the positions of symbols to be de-precoded are matchedwith one another among the antennas, the complexity may be reduced withchannel estimation accuracy maintained.

Referring now to FIG. 9, the detailed configuration of the receiver willbe described. FIG. 9 is a block diagram illustrating the detailedconfiguration of the receiver. As illustrated in FIG. 9, the receiverdiffers from that illustrated in FIG. 5 in that it additionally includesan antenna selection unit 13 d. The antenna selection unit 13 d selectsone of the multiple antennas depending on the arrangement intervals ofpilot signals in the signals transmitted by the antennas and notifiesthe first time-direction interpolation unit 13 b of the selectedantenna.

The first time-direction interpolation unit 13 b then linearlyinterpolates the channel estimation values of symbols corresponding tothe positions of the symbols containing pilot signals from the signaltransmitted by the antenna selected by the antenna selection unit 13 d.

Alternatively, one of the multiple antennas may be selected depending onthe magnitude of time-direction variation in channel estimation valuebetween each transmitting antenna and each receiving antenna, and thechannel estimation values of symbols corresponding to the positions ofthe symbols containing pilot signals, of the selected antenna may beobtained.

For example, in a case where the channel estimation value varies to asmall extent in the time direction, the receiver selects an antennawhose pilot signals are arranged at large intervals, and the positionsof symbols to be de-precoded, of the antennas are matched with those ofthe selected antenna. In this case, the complexity can be furtherreduced. In contrast, in a case where the channel estimation valuevaries to a large extent in the time direction, the receiver selects anantenna whose pilot signals are arranged at small intervals, and thepositions of symbols to be de-precoded, of the antennas are matched withthose of the selected antenna. In this case, even when the transmittedsignal varies to a large extent in the time direction, it is possible toreduce the complexity while maintaining channel estimation accuracy.

Also, in a case where the receiver according to the present invention ismounted on a mobile station, the velocity of the mobile station may bedetected and used as a standard for selecting an antenna according towhich the channel estimation values are obtained. For example, in a casewhere the velocity is low, the receiver selects an antenna whose pilotsignals are arranged at large intervals, and the positions of symbols tobe de-precoded, of the antennas are matched with those of the selectedantenna. In this case, the complexity can be further reduced. Incontrast, in a case where the velocity is high, the receiver selects anantenna whose pilot signals are arranged at small intervals, and thepositions of symbols to be de-precoded, of the antennas are matched withthose of the selected antenna. In this case, even when the transmittedsignal varies to a large extent in the time direction, it is possible toreduce the complexity while maintaining channel estimation andde-precoding accuracies.

The illustrated components of each apparatus do not necessarily need tobe configured physically as illustrated. That is, the specific form ofthe distribution or consolidation of the components of each apparatus isnot limited to what are illustrated, and all or part of the componentsmay be functionally or physically distributed or consolidated in anyunit depending on the loads imposed thereon or the use state thereof.For example, the channel estimation unit 13 and de-precoding unit 15 maybe consolidated.

The channel estimation methods described in the above-mentionedembodiments may be realized by execution of a previously preparedprogram by a computer such as a personal computer or workstation. Thisprogram may be distributed via a network such as the Internet. Thisprogram can also be executed by recording it on a computer-readablerecording medium such as a hard disk, flexible disk (FD), CD-ROM,magneto-optical (MO) disc, flash memory, and DVD and reading it from therecording medium using a computer.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the principlesof the invention and the concepts contributed by the inventor tofurthering the art, and are to be construed as being without limitationto such specifically recited examples and conditions, nor does theorganization of such examples in the specification relate to aillustrating of the superiority and inferiority of the invention.Although the embodiments of the present inventions have been describedin detail, it should be understood that the various changes,substitutions, and alterations could be made hereto without departingfrom the spirit and scope of the invention.

1. A receiver comprising: a channel estimation unit that calculateschannel estimation values of symbols containing pilot signals fromsignals transmitted by a plurality of antennas to obtain channelestimation values of symbols in the same positions of the antennas; ade-precoding unit that de-precodes the channel estimation values of theantennas calculated by the channel estimation unit to calculateeffective channel estimation values; and a time-direction interpolationunit that performs time-direction interpolation using the effectivechannel estimation values calculated by the de-precoding unit tocalculate effective channel estimation values of symbols other than thesymbols containing pilot signals.
 2. The receiver according to claim 1,wherein the channel estimation unit calculates channel estimation valuesof symbols containing pilot signals from the signals transmitted by theantennas as well as, in the signal transmitted by each antenna, linearlyinterpolates channel estimation values of symbols corresponding topositions of symbols containing pilot signals from the signalstransmitted by the other antennas to obtain channel estimation values ofsymbols in the same positions of the antennas.
 3. The receiver accordingto claim 1, wherein the channel estimation unit calculates channelestimation values of symbols containing pilot signals from the signalstransmitted by the antennas as well as linearly interpolates channelestimation values of symbols corresponding to positions of symbolscontaining pilot signals from the signal transmitted by one of theantennas to obtain channel estimation values in the same positions ofthe antennas.
 4. The receiver according to claim 2, wherein the channelestimation unit calculates channel estimation values of symbolscontaining pilot signals from the signals transmitted by the antennas aswell as linearly interpolates channel estimation values of symbolscorresponding to positions of symbols containing pilot signals from thesignal transmitted by one of the antennas to obtain channel estimationvalues in the same positions of the antennas.
 5. The receiver accordingto claim 3, wherein the channel estimation unit includes an antennaselection unit that selects one of the antennas depending on arrangementintervals of pilot signals in the signals transmitted by the antennas,and the channel estimation unit calculates channel estimation values ofsymbols containing pilot signals from the signals transmitted by theantennas as well as linearly interpolates channel estimation values ofsymbols corresponding to positions of symbols containing pilot signalsfrom the signal transmitted by the antenna selected by the antennaselection unit.
 6. The receiver according to claim 4, wherein thechannel estimation unit includes an antenna selection unit that selectsone of the antennas depending on arrangement intervals of pilot signalsin the signals transmitted by the antennas, and the channel estimationunit calculates channel estimation values of symbols containing pilotsignals from the signals transmitted by the antennas as well as linearlyinterpolates channel estimation values of symbols corresponding topositions of symbols containing pilot signals from the signaltransmitted by the antenna selected by the antenna selection unit. 7.The receiver according to claim 1, wherein the channel estimation unitincludes an antenna selection unit that selects one of the antennasdepending on a magnitude of time-direction variation in channelestimation value between a transmitting antenna and a receiving antenna,and the channel estimation unit calculates channel estimation values ofsymbols containing pilot signals from the signals transmitted by theantennas as well as linearly interpolates channel estimation values ofsymbols corresponding to positions of symbols containing pilot signalsfrom the signal transmitted by the antenna selected by the antennaselection unit.
 8. The receiver according to claim 2, wherein thechannel estimation unit includes an antenna selection unit that selectsone of the antennas depending on a magnitude of time-direction variationin channel estimation value between a transmitting antenna and areceiving antenna, and the channel estimation unit calculates channelestimation values of symbols containing pilot signals from the signalstransmitted by the antennas as well as linearly interpolates channelestimation values of symbols corresponding to positions of symbolscontaining pilot signals from the signal transmitted by the antennaselected by the antenna selection unit.
 9. The receiver according toclaim 1, wherein the channel estimation unit includes an antennaselection unit that selects one of the antennas depending on a velocityof a receiver, and the channel estimation unit calculates channelestimation values of symbols containing pilot signals from the signalstransmitted by the antennas as well as linearly interpolates channelestimation values of symbols corresponding to positions of symbolscontaining pilot signals from the signal transmitted by the antennaselected by the antenna selection unit.
 10. The receiver according toclaims 2, wherein the channel estimation unit includes an antennaselection unit that selects one of the antennas depending on a velocityof a receiver, and the channel estimation unit calculates channelestimation values of symbols containing pilot signals from the signalstransmitted by the antennas as well as linearly interpolates channelestimation values of symbols corresponding to positions of symbolscontaining pilot signals from the signal transmitted by the antennaselected by the antenna selection unit.
 11. A communication systemcomprising: a transmitter provided with a plurality of antennas; and areceiver, which includes: a channel estimation unit that calculateschannel estimation values of symbols containing pilot signals fromsignals received from the plurality of antennas to obtain channelestimation values of symbols in the same positions of the antennas, ade-precoding unit that de-precodes the channel estimation values of theantennas calculated by the channel estimation unit to calculateeffective channel estimation values, and a time-direction interpolationunit that performs time-direction interpolation using the effectivechannel estimation values calculated by the de-precoding unit tocalculate effective channel estimation values of symbols other than thesymbols containing pilot signals.
 12. A channel estimation methodcomprising: calculating channel estimation values of symbols containingpilot signals, of signals transmitted by a plurality of antennas toobtain channel estimation values of symbols in the same positions of theantennas; de-precoding the channel estimation values of the antennascalculated by the channel estimation unit to calculate effective channelestimation values; and performing time-direction interpolation using thecalculated effective channel estimation values to calculate effectivechannel estimation values of symbols other than the symbols containingpilot signals.
 13. The receiver according to claim 1, wherein theeffective channel estimation values indicate channel variation betweeneach layer and each receiving antenna.
 14. The communication systemaccording to claim 11, wherein the effective channel estimation valuesindicate channel variation between each layer and each receivingantenna.
 15. The channel estimation method according to claim 12,wherein the effective channel estimation values indicate channelvariation between each layer and each receiving antenna.